Process for dyeing paper with disazo dyes

ABSTRACT

The dyestuffs of the formula ##STR1## in which A, R 1 , M and n are as defined in claim 1, are suitable for dyeing paper with good light-fastness.

Disazo dyes are often used for dyeing paper in blue colour shades. Ifhigh light-fastnesses of the dyeings are desirable, almost exclusivelycopper complexes of dyes are employed in practice. Light-fast blue dyesfor-paper which are not copper complexes have recently been sought foreconomic and ecological reasons. The dyes sought furthermore shoulddisplay a high degree of exhaustion under the specific dyeingconditions, they should produce dyeings with good wet-fastnesses andthey should be so readily soluble that the preparation of liquidcommercial forms, i.e. concentrated solutions of these dyes, ispossible. These conditions are not yet met in all respects by the bluedyes for paper which are currently obtainable.

The present invention was based on the object of providing a process fordyeing paper in blue colour shades in which the requirements mentionedare met as far as possible. This object is achieved by the processaccording to the invention.

The invention relates to a process for dyeing paper, which comprisesusing a dye of the formula ##STR2## in which A is a radical of theformula ##STR3## X and Y independently of one another are hydrogen,alkyl, alkoxy or --NH--CO--Z,

Z is hydrogen, alkyl, aryl, alkoxy, amino, mono- or dialkylamino orarylamino,

R₁ is hydrogen, alkyl, alkoxy, halogen, SO3M or carboxyl,

M is hydrogen or one equivalent of a colourless cation,

n is 1 or 2 and

m is0or 1.

Alkyl radicals are generally to be understood, according to theinvention, as meaning straight-chain, branched or cyclic alkyl groups.Cycloalkyl preferably contains 5 to 8 C atoms and open-chain alkylpreferably contains 1 to 8 C atoms.

Unbranched or branched open-chain alkyl is, for example: methyl, ethyl,n- and iso-propyl, n-, sec- or tert-butyl, n- and iso-pentyl, n- andiso-hexyl or 2-ethylhexyl.

These alkyl radicals can be mono- or polysubstituted, for example byhydroxyl, sulfo, carboxyl, C₁ -C₄ alkoxy, hydroxyl-substituted C₁ -C₄alkoxy, phenyl, phenoxy or phenylaminocarbonyl, it being possible forthe phenyl group in the last three radicals mentioned to be substituted,for example by sulfo, C₁ -C₄ alkyl, C₁ -C₄ alkoxy or phenoxy. Suitableradicals of this type are, for example: hydroxyethyl,1-hydroxy-isopropyl, ethoxymethyl, 2-hydroxyethoxypentyl, benzyl,1-phenylethyl, 2-phenylethyl, 1-methyl-2-phenylethyl,1-iso-butyl-3-phenylpropyl, 1,5-diphenyl-3-pentyl,1-methyl-2-phenoxyethyl or 1 -methyl-2-phenylaminocarbonyl-ethyl.

Cycloalkyl is, in particular, cyclopentyl and cyclohexyl; substituentsare, in particular, C₁ -C₄ alkyl, especially CH₃.

Suitable alkoxy radicals are preferably those having 1 to 4 C atoms, forexample methoxy, ethoxy, propoxy, iso-propoxy, n-butoxy, iso-butoxy ortert-butoxy. These alkoxy radicals can be substituted, for example bythe radicals mentioned as substituents of the alkyl groups, inparticular by hydroxyl or C₁ -C₄ alkoxy. Substituted alkoxy radicalsare, for example, hydroxyethoxy, methoxyethoxy, 2-hydroxypropoxy,1,2-dihydroxy-3-propoxy or 1,2-dimethoxy-3-propoxy.

Halogen is to be understood as meaning fluorine, bromine, iodine or, inparticular, chlorine.

Aryl radicals in this Application are generally to be understood asmeaning aromatic or heteroaromatic radicals, but especially naphthyl orin particular phenyl radicals. All these radicals can be unsubstitutedor substituted. Substituents are, for example, C₁ -C₄ alkyl, C₁ -C₄alkoxy, bromine, chlorine, nitro, cyano, sulfo, carboxyl or C₁ -C₄alkylcarbonylamino. However, the particularly preferred meaning of arylis phenyl.

M is hydrogen or one equivalent of a colourless cation, for examplelithium, sodium, potassium, ammonium or the protonated form of a C₄ -C₁₂trialkylamine, C₄ -C₁₂ diamine or C₂ -C₁₅ alkanolamine.

A protonated C₄ -C₁₂ trialkylamine M can be, for example, protonatedN-ethyldimethylamine, N,N-diethylmethylamine, tri-n-propylamine,tri-n-butylamine, tri-isobutylamine and, in particular, triethylamine ortri-isopropylamine; mixtures of different protonated amines are alsosuitable.

A protonated C₄ -C₁₂ diamine M is, for example, an ethylenediamine or1,3-diaminopropane, in which one or both N atoms are additionallysubstituted by one or two C₁ -C₄ alkyl radicals, preferably methyl orethyl radicals. M here is preferably an N,N-dialkylethylenediamine orN,N-dialkyl-1,3-diaminopropane. Examples are: N-ethylethylenediamine,N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine,N,N-diethylethylenediamine, 3-dimethylamino-1-propylamine or3-diethylamino-1-propylamine.

A protonated C₂ -C₁₅ alkanolamine M can be, for example, the protonatedform of a monoalkanol-, dialkanol-, monoalkanolmonoalkyl-,monoalkanoldialkyl-, dialkanolalkyl-or trialkanolamine or a mixture ofdifferent protonated alkanolamines. Examples are protonated2-aminoethanol, di(2-hydroxyethyl)amine,N-(2-hydroxyethyl)dimethylamine, N-(2-hydroyethyl)diethylamine,N,N-di(2-hydroxyethyl)methylamine, N,N-di(2-hydroxyethyl)ethylamine ortri(2-hydroxyethyl)amine, 2-aminoethoxyethanol ordiethylaminopropylamine. Protonated polyglycolamines are also possible,for example diethanolamine tris-glycol ether.

M is preferably Na.sup.⊕, Li.sup.⊕ or a protonated C₄ -C₆ alkanolamine,preferred C₄ -C₆ alkanolamines being tri(2-hydroxyethyl)amine,di(2-hydroxyethyl)amine or a mixture of these two amines.

Z is preferably C₁ -C₄ alkyl, substituted or unsubstituted phenyl, aminoor substituted or unsubstituted phenylamino, in particular methyl,phenyl, amino or phenylamino.

X and Y are preferably hydrogen, methyl, methoxy, acetylamino,benzoylamino, ureido or phenylureido, in particular hydrogen, methyl ormethoxy.

R₁ is, in particular, hydrogen, methyl, methoxy, chlorine, SO₃ M orcarboxyl, especially hydrogen or SO3M.

A particularly preferred embodiment of the process according to theinvention comprises using a dye of the formula ##STR4## in which X and Yindependently of one another are hydrogen, methyl, methoxy or--NH--CO--Z,

Z is methyl, phenyl, amino or phenylamino,

R₁ is hydrogen, methyl, methoxy, chlorine or SO₃ M,

M is hydrogen or one equivalent of a colourless cation and

n is 1 or2.

Among these, particularly preferred dyes are those of the formula##STR5## in which X and Y independently of one another are hydrogen,methyl or methoxy,

R₁ is hydrogen or SO₃ M and

M is hydrogen or one equivalent of a colourless cation.

The dyes of the formula (1) used in the process according to theinvention for dyeing paper are known or can be prepared in a mannerknown per se. However, these dyes have previously been used only fordyeing cotton. Surprisingly, they are particularly suitable for dyeingpaper and are particularly distinguished in this context by a goodlight-fastness of the resulting dyeings.

In recent years, the use of concentrated aqueous solutions of dyes hasgained in importance, in particular because of the advantages which suchsolutions have over dyes in powder form. By using solutions, thedifficulties associated with dust formation are avoided and the user isfreed from the time-consuming and often difficult dissolving of the dyepowder in water. The use of concentrated solutions furthermore has beenprompted by the development of continuous dyeing processes for paper,since in these processes it is advantageous to add the solution directlyto the Hollander or at any other suitable point of papermaking.

However, difficulties frequently occur when concentrated aqueoussolutions of anionic dyes are used, since such solutions are notsufficiently storage-stable and precipitates occur during storage forseveral months, in particular at about 0° to 5° C.

It has now been found that concentrated aqueous solutions of the dyesused according to the invention have a very good storage stability ifthey comprise at least 0.1 mol of Li.sup.⊕ per mol of dye of the formula(1), the solutions preferably having a pH of at least 11.

The invention therefore also relates to aqueous solutions of dyes, whichcomprise 2 to 20 per cent by weight of a dye of the formula ##STR6## andat least 0.1 mol of Li.sup.⊕ per mol of dye of the formula (1), in whichA, M, R₁ and n are as defined above under the formula (1).

Among these, those which have a pH of at least 11, preferably between 11and 13, are preferred.

Preferred aqueous dye solutions comprise 6 to 15 per cent by weight of adye of the formula (1) and 0.1 to 3 mol of Li.sup.⊕ per mol of dye ofthe formula (1) and have a pH of at least 11.

Those dye solutions which comprise less than 2% by weight, based on theweight of the dye solution, of inorganic salts furthermore arepreferred. If the dye solutions are obtained with a higher salt contentduring synthesis, the solutions can be desalinated in the customarymanner, for example by a membrane separation process.

The pH of at least 11 is established in the dye solutions according tothe invention by addition of a strong base, for example NaOH, KOH,ammonium, diethanolamine or triethanolamine, but preferably LiOH.

The dye solutions according to the invention can additionally comprisewater-soluble organic solubilizing agents, for example urea,ε-caprolactam, dimethyl sulfoxide, N-methylpyrrolidone, water-misciblepolyhydric alcohols, such as ethylene glycol, propylene glycol orglycerol, alkanolamines, such as ethanolamine or triethanolamine, orpolyglycolamines, for example reaction products of ammonia, as well asalkyl- and hydroxyalkylamines with alkylene oxides, such as ethyleneoxide, 1,2-propylene oxide, 1,2-butylene oxide or 2,3-butylene oxide, insuitable quantitative ratios. Such polyglycolamines are known, forexample from DE-A-2 061 760.

The concentrated aqueous solutions according to the invention of dyes ofthe formula (1) can be prepared, for example, by a procedure in whichthe dye suspension obtained during preparation of the dye is filtered,desalinated, for example by a membrane separation process, ifappropriate, and stabilized by addition of a lithium salt and/or lithiumhydroxide and if appropriate a solubilizing agent. However, the isolateddye can also be suspended in hydrochloric acid filtered again and thefilter cake can be mixed with lithium hydroxide and/or a suitablelithium salt and the required amount of water. Finally, the coupling canalso be carried out in the presence of LiOH or alkanolamines and thesynthesis solution can then be desalinated.

The aqueous dye solutions according to the invention, which are stableat storage temperatures down to -5° C., are suitable for dyeing paper,on which they produce attractive blue colour shades with highlight-fastness with or without the use of a size.

The dye solutions can be used by all the processes customary in thepaper industry for direct dyes, in particular for pulp as well assurface dyeing of paper for sized and non-sized grades, starting frombleached or unbleached cellulose of various origins, such as softwood orhardwood sulfite and/or sulfate cellulose.

The present invention furthermore relates to the dyes of the formula##STR7## in which X is hydrogen, alkyl, alkoxy or --NH--CO--Z,

Y' is a C₁ -C₄ alkoxy radical, which is substituted by hydroxyl, C₁ -C₄alkoxy, sulfo, carboxyl, phenyl, phenoxy or phenylaminocarbonyl,

Z is hydrogen, alkyl, aryl, alkoxy, amino, mono- or dialkylamino orarylamino,

R₁ is hydrogen, alkyl, alkoxy, halogen, SO₃ M or carboxyl,

M is hydrogen or one equivalent of a colourless cation,

n is 1 or 2 and

m is0or 1.

X, Z, R₁, M, n and m are preferably as defined as preferred in the dyesof the formula (1), and Y' is preferably C₁ -C₄ alkoxy which issubstituted by hydroxyl or methoxy.

The novel dyes of the formula (6) can be prepared in a manner known perse, for example by diazotization of an aminoazo compound of the formula##STR8## and coupling of the product with a compound of the formula##STR9##

In the compounds of the formulae (7) and (8), X, Y', M, n and R₁ are asdefined under formula (6).

In the following examples, parts are by weight and temperatures arestated in degrees Celsius.

EXAMPLE 1

60.8 g of the compound of the formula ##STR10## are dissolved withsodium hydroxide solution in 350 ml of water together with 6.9 g ofsodium nitrite under neutral conditions and diazotized by addition of19.2 g of 32% hydrochloric acid at 20° to 25° C. The resulting diazosuspension is added dropwise in the course of 45 minutes, at 25° to 30°C., to a solution prepared from 34.8 g of6-anilino-1-hydroxynaphthalene-3-sulfonic acid and 22 g ofdiethanolamine in 250 ml of water; during this operation, the pH is keptat 8.5 to 9.0 by addition of 18.0 g of diethanolamine. When the couplinghas ended, 40 g of 50% sodium hydroxide solution are added to thesynthesis solution and hydrolysis is carried out at 75° C. for one hour.After cooling to room temperature, the pH is brought to 6.5 to 7 with32% hydrochloric acid. A suspension containing the dye of the formula##STR11## is obtained.

The dye suspension is desalinated by reverse osmosis over a membrane ofchemically modified polyacrylonitrile at 50° C. and concentrated to afinal weight of 750 g.

A liquid formulation which is storage-stable at 2° to 5° C. for severalmonths is obtained.

EXAMPLE 2

A dye suspension containing 85.9 g of the trisodium salt of the dyedescribed in Example 1 is prepared as described in Example 1, exceptthat 29 g of 30% sodium hydroxide solution are used instead of 40 g ofdiethanolamine. The resulting suspension is then desalinated by reverseosmosis over a membrane of chemically modified polyacrylonitrile at 50°C. and concentrated to a final weight of 750 g. 3.9 g of LiOH.1H₂ O and3.9 g of anhydrous Li₂ SO₄ are added and the solution is stirred at 50°C. for one hour. It is then cooled to 25° C., made up to 780 g withdeionized water and filtered.

The resulting dye solution is stable for several months at a storagetemperature of 2° to 5° C. and dyes paper with excellent light-fastness.

EXAMPLE 3

The procedure described in Example 1 is repeated, except that 11.7 g ofanhydrous Li₂ SO₄ are used in place of 3.9 g of LiOH.1H₂ O and 3.9 g ofanhydrous Li₂ SO₄, likewise affording a storage-stable liquidformulation.

EXAMPLE 4

The procedure described in Example 1 is repeated, except that a total of9.9 g of LiOH.1H₂ O is used for the coupling in place of diethanolamine,likewise affording a storage-stable liquid formulation.

EXAMPLE 5

70 parts of chemically bleached sulfite cellulose (from softwood) and 30parts of chemically bleached sulfite cellulose (from birch wood) arebeaten in 2000 parts of water in a Hollander. 2.5 parts of the dyesolution described in Example 1 are added to this pulp. After a mixingtime of 20 minutes, paper is produced from this pulp. The absorbentpaper obtained in this manner is dyed blue. The dyeing has a highlight-fastness. The waste water is practically colourless.

EXAMPLE 6

3.0 parts of the dye solution from Example 1 are dissolved in 100 partsof water and the solution is added to 100 parts of chemically bleachedsulfite cellulose which has been beaten with 2000 parts of water in aHollander. After thorough mixing for 15 minutes, sizing is carried outin the customary manner with resin size and aluminium sulfate. Paperproduced from this pulp has a blue shade with good wet-fastnesses andgood light-fastness.

EXAMPLES 7-13

The following dyes which dye paper in blue colour shades with goodfastnesses are prepared in a manner analogous to that described inExample 1.

    ______________________________________                                         ##STR12##                                                                    Example   A                                                                   ______________________________________                                         7                                                                                       ##STR13##                                                           8                                                                                       ##STR14##                                                           9                                                                                       ##STR15##                                                          10                                                                                       ##STR16##                                                          11                                                                                       ##STR17##                                                          12                                                                                       ##STR18##                                                          13                                                                                       ##STR19##                                                          ______________________________________                                    

EXAMPLES 14-16

The following dyes which dye paper in blue colour shades with goodfastnesses are prepared in a manner analogous to that described inExample 1.

    __________________________________________________________________________     ##STR20##                                                                               Example                                                                            R                                                             __________________________________________________________________________               14   CH.sub.3                                                                 15   SO.sub.3 H                                                               16   COOH                                                          __________________________________________________________________________

EXAMPLES 17-22

The following dyes which dye paper in blue colour shades with goodfastnesses are prepared in a manner analogous to that described inExample 1.

    ______________________________________                                         ##STR21##                                                                    Beispiel  A                                                                   ______________________________________                                        17                                                                                       ##STR22##                                                          18                                                                                       ##STR23##                                                          19                                                                                       ##STR24##                                                          20                                                                                       ##STR25##                                                          21                                                                                       ##STR26##                                                          22                                                                                       ##STR27##                                                          ______________________________________                                    

EXAMPLES 23-25

The following dyes which dye paper in blue colour shades with goodfastnesses are prepared in a manner analogous to that described inExample 1.

    ______________________________________                                         ##STR28##                                                                    Example     D                                                                 ______________________________________                                        23                                                                                         ##STR29##                                                        24                                                                                         ##STR30##                                                        25                                                                                         ##STR31##                                                        ______________________________________                                    

What is claimed is:
 1. An aqueous solution of a dye having a pH of atleast 11 which comprises 2 to 20 per cent by weight of a dye of theformula ##STR32## and at least 0.1 mol of Li.sup.⊕ per mol of dye of theformula (1), in whichA is a radical of the formula ##STR33## wherein Xis hydrogen, C₁ -C₈ -alkyl, C₅ -C₈ -cycloalkyl, C₁ -C₄ -alkoxy, or--NH--CO--Z, Y is C₁ -C₄ -alkoxy which is unsubstituted or substitutedby hydroxyl, C₁ -C₄ -alkoxy, sulfo, carboxyl, phenyl, phenoxy orphenylaminocarbonyl, Z is hydrogen, C₁ -C₈ -alkyl, C₅ -C₈ -cycloalkyl,naphthyl, phenyl, C₁ -C₄ -alkoxy, mono- or dialkylamino, naphthylaminoor phenylamino, R₁ is hydrogen, C₁ -C₈ -alkyl, C₅ -C₈ -cycloalkyl, C₁-C₄ -alkoxy, halogen, SO₃ M or carboxyl, M is hydrogen or one equivalentof a colorless cation, and n is 1 or2.
 2. An aqueous solution of a dyeaccording to claim 1, which comprises 6 to 15 per cent by weight of adye of the formula (1) and 0.1 to 3 mol of Li.sup.⊕ per mol of dye ofthe formula (1) and has a pH of at least
 11. 3. An aqueous solution of adye according to claim 1, which further comprises less than 2% byweight, based on the weight of the dye solution, of inorganic salts. 4.An aqueous solution of claim 1 wherein the pH is between 11 and 13.